JPS5869489A - Drive circuit for dc motor - Google Patents

Abstract

PURPOSE:To prevent the damage of a transistor or the like by converting the rectangular wave output from the position detector of a rotor via a trapezoidal wave generator to a trapezoidal waveform and switching and energizing a coil, thereby reducing the counterelectromotive force generated in the coil. CONSTITUTION:A DC motor is formed of a disc-shaped yoke 1, an energizing coil 3 and a disc-shaped magnet 2 of a rotor. The position of the rotor is detected by a Hall element 6A, is amplified by a differential amplifier 16 to a rectangular wave, is then added to a trapezoidal wave generator 14 including transistors 18, 19 forming high gain differential amplifier, a condenser C and an emitter follower 21 to be added to energization switching means 7, and the current from a control current generator 11 is alternately switched to energize the coil 3. Accordingly, the switching operation is gradually started to slowly break, thereby reducing the counterelectromotive force. In this manner, the damage of the transistors can be prevented, and the circuit can be reduced in size.

Description

[Detailed Description of the Invention] The present invention relates to a drive circuit for a DC motor.
More particularly, the drive circuit K suitable for IC (integrated circuit)
r1i.

Now, it comprises at least two energizing coils, a magnetic plate having a N-pole region and an 8-pole region, and energization switching means for alternately switching and supplying direct current to the two energizing coils,
Due to the interaction between the current flowing through the energized coil and the magnetic flux generated by $P on the magnet plate, the magnet plate rotates as a rotor relative to the energized coil, and according to the relative rotational position of the skeleton magnet plate with respect to the energized coil, the magnet plate rotates as a rotor. For example, a DC motor in which the magnet plate continues to rotate as a rotor by controlling the energization switching operation by the energization switching means is used.
It is known as a cylinder drive motor in a magnetic dual image reproduction device (VTR).

FIG. 1(a) is a side view showing the basic structure of such a conventional DC motor, and FIG. 1(b) is a top view of the same.

In these figures, 1 is a disc-shaped magnet, 2 is a disc-shaped magnet, and 3A, 3B, 4A, and 4BFi are the first
It is a current-carrying coil as shown in the perspective view in Figure A.
#'i axis. FIG. 1(B) is a top view of the magnet plate 2. If the magnet plate 2 were to be transparent, the current-carrying coils 3A, 3B and 4M, as shown by dotted lines,
You should see that 4B is placed on top of the cover 1. As shown in FIG. 1A, each energizing coil is made of a small triangular plastic core K which is wound around a triangular core.

As shown in FIG. 1B, the magnetized regions in the disk-shaped magnet plate 2 are arranged at an angle of 60 degrees around the center point, such as N, S, zero,
There are N, S, and zero regions. Note that the zero region is a non-magnetized region, but it actually consists of a weak (8) region and a weak (N) region divided as shown by dotted lines.

The coils 3M and 3B form one set, and the coils 4A and 41 form another set9, and the DC current is switched and energized for each set. A closed magnetic path is constructed from the magnet plate 2 through the yoke 1, so this magnetic flux and the energized coil (for example, 3mm and 3mm
The interaction with the direct current flowing in B) generates ff) torque, in which case the magnet plate 2 rotates together with the shaft 5 since the energizing coil on the shaft 1 is fixed. Depending on the rotational position of the magnet plate 2, for example, the energized coils 3A and 38
When the direct current that was being used in 1liK& is switched to the pair of current-carrying coils 4A and 4B, the rotating operation of the magnet plate 20 as a rotor continues, but regarding this rotating operation, a.
I will explain later.

In No. 11111, when the magnet plate 2 is rotated in the direction of the arrow, the view 51 is obtained at a fixed point P on the periphery of the magnet plate 2.
The change in magnetic flux density caused by -g is as shown in Fig. 2 (support). That is, a positive magnetic flux density is observed in the N region, a negative magnetic flux density is observed in the S region 'e, and weak positive and negative magnetic flux densities are observed in the zero region.

The waveform shown in Figure 2 (F) is schematically shown in Figure 2 (B).
The result will be as shown below. If we place a Hall element that converts the magnetic field strength (a flux band R) into an electrical quantity at point P and observe its output waveform (Figure 2 () and #'i (b)), we can conversely determine the Since the rotational position of the magnet plate 2 can be known, such a Hall element can be used as a rotational position detector of the rotor.

Now, in the conventional DC motor as outlined above,
The rectangular wave output from the rotor's rotational position detector (the frame is a Hall element) (more precisely, in Figure 2) is a distorted waveform as shown in K, but if this is amplified, it becomes a rectangular wave. The energization was switched between the two sets of energizing coils using the rectangular wave output. Please explain this specifically #I
This will be explained with reference to FIG.

FIG. 3 is a circuit diagram showing a conventional DC motor drive circuit. In the figure, 6 is a rotational position detector of the rotor such as a Hall element, 7 is an energization switching means, 8a and sba are each drive transistors, 9m and 9b are capacitors, 3
and 4ti are the current-carrying coils, and 10 is the voltage for the motor. In addition, the control current generating circuit 11t is a circuit that controls the current flowing through the coil 3 or 4 by the switching action of the energization switching means 7 so that the rotational speed of the motor is constant. The rectangular wave output from the detector 6 activates the coil 3.40 sequential switching energizing means 7, amplifies the current from the control current generation circuit 11 with the drive transistor sa*gb, and sequentially outputs a rectangular wave to the coil 3.4. Electrifies as an electric current. Figure 4 (0) shows the base and sumi pressure waveforms of drive transistors 8m and 8b, and 13 shows the collector voltage waveforms (when content is 9m and 9b is not present), respectively. The collector voltage waveform 13
As can be seen, when the current to the coil 3.4 is abruptly cut off, that is, when the drive transistors 8a and 8b are abruptly cut off, the back electromotive force generated in the coil 3.4 and the motor voltage 10 are The sum voltage causes the transistor 8a,
IIK supplied current causes the transistor 8 a
Due to the voltage drop occurring in the off-resistance at t 8 b, the collector potential rises rapidly as shown at 13 in FIG. 4 ←). This potential increase causes the potential to rise beyond the collector-emitter withstand voltage limit of the drive transistors 8m, 8b, and there is a possibility that the drive transistors 8m, 8b may be destroyed. To prevent this, in the circuit example shown in Figure 1lE1, a large capacitance contactor is installed between the collector and emitter. 9m and 9b are attached. In another example, in addition to the collector-emitter capacitor, there is also a relatively small capacitor between the collector base. Therefore, when thinking about using an IC for the drive circuit of a DC motor, I decided to use a large-capacity converter. has the disadvantage of being unsuitable for IC implementation.The purpose of the present invention is to improve the above-mentioned disadvantages of the prior art, and to reduce the amount of electricity generated at the ends of the coil due to K when the coils are sequentially switched and energized gradually and slowly cut off. It is an object of the present invention to provide a DC motor drive circuit that can reduce the back electromotive force caused by the output stage and eliminate the capacitance provided in the output stage or reduce the capacitance value.

In the present invention, a trapezoidal wave is generated from the rectangular wave output instead of directly inputting the rectangular wave output with steep rise and fall from the rotor position detector to the coil sequential energization switching means. The above object is achieved by providing means for sequentially energizing the coils with the trapezoidal wave, and sequentially energizing the coils with the control current in the trapezoidal waveform.

Next, an embodiment of the present invention will be described with reference to the drawings.

Figure 5 shows the rotation JIUI of the DC motor as outlined above.
FIG.

In the same figure, a magnet plate 2 and two sets of current-carrying coils (3 mm,
In order to easily distinguish the relative positional relationship between 3B and 4B, a magnet plate 2 is shown in the center and a current-carrying coil is placed around it.

In FIG. 5, reference numeral 6 indicates a rotor rotational position detector (for example, a Hall element);
As explained in detail with reference to Figure B, the winding angle f of each coil (3mm, 3m, 4A, 4B) is 60 degrees, and the interval between adjacent coils is 30 degrees. and
The magnet plate 2 becomes the rotor. First, as shown in No. 5 WJ (a) K, when a current flows through the coil 4 as shown by the arrow, the coil part where the outward current flows and the central current flows. , 7 According to Lemming's left hand rule, a clockwise rotational torque is generated. However, since the coils 3 (Im, Im) and 4 (A, B) are fixed, the magnet plate 2 will rotate counterclockwise.・When the magnet plate 2 moves by 30 degrees in terms of position angle, , Figure 5 (b
) The positional relationship will be as shown in (). Here, if the coil 3B is energized as shown by the arrow, torque will be generated in the portion of the coil through which the outward current flows, and the rotational motion will be maintained. ((In Fig. 5(c), which has been rotated by 90 degrees in position angle, by energizing the coil 3B, torque is generated in the part of the coil where the current flows toward the center, and the rotational motion is maintained.) , electrical angle 360 degrees, i.e. position angle 180 degrees
Looking at the degrees, it can be seen that the magnet plate 2 always rotates counterclockwise.

Here, the reason why there are 211 coils 3 and 4, M and B, respectively, is to increase rotational efficiency.

33#'i shown in FIG. 6(f) is a waveform diagram showing the output waveform of the position detector 6 in FIG. 5, which was previously explained with reference to FIG. 2. The zero region of the magnet plate 2 is weak so that the magnetic flux density changes smoothly from the %N# region to the S〃 region (as explained earlier, S and N are magnetized). .

By providing magnetic flux distortion means (existence of zero region) on the magnet plate 2, as seen from the output waveform 33, the electrical angle 3
There is no point where the composite rotational torque becomes zero at 60 degrees, but since it is technically difficult to create a trapezoidal wave with the same slope at the direct rise and fall of the V output waveform 33, After converting into a rectangular wave as shown at 34 in FIG. 6(cl), it is preferable to create a trapezoidal wave 35 as shown in FIG. 6(f).

FIG. 7 is a block diagram showing one embodiment of the present invention, JIIfII. In the figure, KFi, which is the same as in Figure 3, is shown.
Although the same reference numerals are given, 14 is a trapezoidal wave generating circuit, and 15m and 15b are current amplifiers, respectively.

In FIG. 7, the trapezoidal wave generating circuit 14, which receives the rectangular wave output from the rotor rotational position detector 6, creates and outputs a trapezoidal wave, thereby activating the energization switching means 7. Alternately with current amplifier 15m + 15b,
The current from the control current generation circuit 11 is amplified and supplied to the coils 3 and 4 as trapezoidal wave currents, respectively.

FIG. 8 is a specific circuit diagram showing one embodiment of the present invention.

In the figure, a Hall element 6m is used as a rotational position detector of the rotor. In addition, 16 is a differential amplifier,
17 is a constant current source (current value l of constant current), 18, 19.
20 is a transistor, 21#i is a follower circuit, 23 and 24 are transistors, and 25 is a power supply.

In FIG. 8, the output of the Hall element 6A is transferred to the differential amplifier 1.
6, the signal is amplified into a rectangular wave and sent to the trapezoidal wave generating circuit 14. The trapezoidal wave from the control current generating circuit 14 activates the current switching means 7 (in this example, a differential switching circuit consisting of transistors 23 and 24 whose base input is the trapezoidal wave output), and the current from the control current generating circuit 11 is activated. is alternately switched and supplied to current amplifiers 15m and 1.5b (here, the base current of the Darlington-connected transistor). In this way, the current obtained by amplifying the trapezoidal input current is applied to the coils 3 and 4.

Next, we will explain the details of the trapezoidal wave generation circuit 14 @differential amplification!
! Input the two outputs from s16 to the bases of transistors 18 and 19 that constitute the high gain differential amplifier *17a constant current source (current value Xo), DIFi diode, J*R
2 is a resistor, and 2o is a transistor. The output of the high gain differential amplifier is output from point Q where the collectors of transistors 20 and 19 are connected. Therefore, it has a high output impedance. According to transistor 190 on and off, capacitor? Charging and discharging are performed via the CKIC terminal 22. The IC terminal 22 is a terminal necessary for externally connecting the capacitor C69, and is not directly related to the present invention.

The charging and discharging path to the capacitor C is explained in an easy-to-understand manner as follows. First, when the transistor 18 is on, a current flows through the diode D1 and the resistor RIK, so the transistor 20 is also turned on, and current also flows through the transistor 20 and the resistor R2. The current at this time is the current obtained by discharging the capacitor C. Conversely, when the transistor 19 is on, the transistor 18 is turned off, and the current no longer flows through the diode D1, the resistor R, and Ktj, so the transistor 20 is also turned off. Therefore, constant current source 1
Is the current flowing from transistor 7 through transistor 19 content? It flows into C and charges it. At this time, since the output impedance of the differential amplifier is large, it can be considered that charging and discharging occurs equivalently through a current source. When charging and discharging the capacitor C through a current source, the time and the amount of charge charged and discharged are proportional.

In other words, content? When the capacitance of C is 00, the amount of charge stored in the capacitor is Q, and the voltage across the capacitor is V, the following equation holds true.

Q-ICo■ ・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・(
1) Therefore, by transforming this, we obtain the following equation.

However, 1 is the current flowing into the capacitor, but in this case, 1 constant current IO''t'1!, so if we rewrite the above equation (2), we get the following. However, t is time.

From the above equation (3), the voltage V across capacitor C is:
On the other hand, the voltage divided by the bias resistors R,,a is used to operate the vine follower 24 to create a reference voltage source. Then, in the scimitar diode D2eD5, the voltage other than the content tC rises or falls, and the reference voltage ±vy (however, v
A limiter is applied at a point where the voltage drop due to y#i diode D2°D is reached. This creates a trapezoidal wave.

Reference numeral 36 shown in FIG. 9(a) is a waveform diagram showing the generated trapezoidal wave. Its amplitude 37 is 2VF, and its center potential is the output potential of the constructional vine follower 21. ss and 39tf shown in Figures 9 (b) and (c), current flowing through coil 3.4, respectively, 40°41Fi shown in Figures 9) and 2), coil 3°4 when speed control is applied, respectively. It also shows the potential generated elsewhere (in this example, the collector potential of the Darlington-connected transistor). It can be seen that no sudden potential rise occurs. Furthermore, if the current value I0 from the constant current source 17 is made small, the capacitance value of the capacitor C connected from the terminal 22 outside the IC circuit can also be made small, which is convenient.

According to the present invention, the coils are sequentially switched and energized using a trapezoidal wave, so that the switching operation of energization is gradually started and then slowly cut off, and the back electromotive force generated in the coil can be reduced. External attachment is effective in preventing damage and reducing capacity.

[Brief explanation of drawings]

Figure 10) shows the basic configuration of a conventional DC motor.
i-side view, Figure 1 0:I) is the same upper view, Figure 1A is a perspective view of the current-carrying coil, Figure 1B is an explanatory diagram of the magnetized region on the magnet plate, Figure 2 (() is In the figure, when the magnet plate 2 is rotated in the direction of the arrow !lc, the surrounding fixed points PK
Figure 2 (b) is a waveform diagram that schematically shows the change in magnetic flux density observed in The signal waveform diagram of the main part in the circuit of Figure 3, Figure 5 is a diagram explaining the rotation principle of the DC motor, Figure #I6 is the output waveform diagram of the same rotation position detector 6 in Figure 5, and Figure 7m is the diagram of the output waveform of the rotary position detector 6 in Figure 5. FIG. 8 is a block diagram showing one embodiment of the present invention, FIG. 8 is a specific circuit diagram showing one embodiment of the present invention, and FIG. 9 is a waveform diagram of various signals in the circuit of FIG. 2- Magnet plate, 3.4... Coil, 5-
Transport, 6-rotational position detector, 7... energization switching means, 8-
・・Drive transistor, 9～・Capacitor, 1o・・
Motor voltage, 11 - control current generation circuit, 12...
Drive transistor 80 base voltage waveform, 13... Collector voltage waveform, 14-... Trapezoidal wave generation circuit, 15...
Current amplifier, 16... Differential amplifier, 17... Constant current source, 18.19.20... Transistor, 21...
Emitter CI'), 22-IC111 child, 23.24
-) Transistor, 25-・Power supply, 33.34.35...
- Output waveform of rotational position detector 6. Agent Patent Attorney Akio Namiki Figure 1 (A) (W) 7
Figure A Figure 1B Figure P Figure 2 Figure 3 Figure 4 Figure 5 (a) (b) (c) Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] 1) A current-carrying coil comprising at least two current-carrying coils, a magnetic plate having an N-pole region and a S-pole region, and a current-carrying switching means for alternately switching and supplying direct current to the two current-carrying coils. Due to the interaction between the current flowing through the magnetic plate and the magnetic flux generated in the magnetic plate, the magnetic plate rotates as a rotor relative to the current-carrying coil, and the relative rotational position of the magnetic plate with respect to the current-carrying coil can be obtained from a detector. In the DC motor, the rotational position input to the energization switching means is controlled in accordance with the position detection signal inputted to the energization switching means. The position detection signal from the device is provided with a trapezoidal wave instead of a rectangular wave, so that when switching the energization, instead of discontinuously switching the energization from one coil to the other, the current is kept in the energized state 11 until then: The energization switching is controlled in a continuous manner so that the current in the coil that was previously in the non-energized state is gradually reduced to reach a non-energized state, and at the same time, the current in the coil that was previously in a non-energized state is gradually increased to reach a energized state. A DC motor drive circuit characterized by: